1. Field of the Invention
The present invention relates to a portable information terminal.
2. Description of the Related Art
With the advent in recent years of small, lightweight information-handling devices, it has been increasingly popular to use portable information terminals which may be connected to a mobile telephone set, for example, by a cable for outdoor data communications by sending and receiving e-mail and browsing home pages on the Internet. Such portable information terminals include laptop personal computers and personal digital assistants that are finding growing usage because of easy-to-use operating systems incorporated therein. The portable information terminals may also be used for on-line shopping, global positioning, and route guidance as well as browsing home pages and sending and receiving e-mail.
Portable information terminals are convenient for use in outdoor applications where access to wired communications is limited, and can be used for data communications anytime and anywhere, even while in motion.
Since portable information terminals are primarily used for data communications, they have an input unit for inputting information to be sent and a display unit for displaying received information. Generally, portable information terminals are larger in size than mobile telephone sets that mainly serve the purpose of speech communications, and are battery-operated for a period of time which is shorter than the standby time of the mobile telephone sets. Because the portability of portable information terminals is an essential feature to be maintained, it is not desirable for portable information terminals to be accompanied by large batteries. Therefore, there is a limitation on efforts to increase the battery-operated time of a portable information terminal by increasing the capacity of the battery thereof. Accordingly, it is important to make portable information terminals usable on batteries for as long a period of time as possible by reducing the power consumption by the portable information terminals. One approach to the reduced power consumption is to turn off the portable information terminal to save electric energy while the portable information terminal does not need to operate.
For data communications, the user of a portable information terminal often places the portable information terminal in a standby mode waiting for incoming data so that it can receive e-mail anytime. The portable information terminal needs to be in the standby mode so as to be ready for operation anytime in case of the arrival of incoming data while at the same time saving electric energy.
FIG. 1 of the accompanying drawings is a block diagram of an arrangement of a conventional portable information terminal.
As shown in FIG. 1, portable information terminal 3 is connected to potable telephone set 2 by connector 31, and exchanges data to be sent and received data and control information with potable telephone set. While in a standby mode, portable information terminal 3 turns off controller 33 and information processor 34 in order to minimize power consumption by portable information terminal 3. However, connector 31 is kept in operation at all times because it is necessary for portable information terminal 3 to receive an indication of data reception from mobile telephone set 2. Therefore, portable information terminal 3 continuously consumes electric energy sufficient to operate connector 31 even in the standby mode.
The conventional portable information terminal that consumes electric energy in the standby mode is not preferable in view of the requirement for a long period of time in which it can be used on the battery.
It is therefore an object of the present invention to provide a portable information terminal which does not consume electric energy while in a standby mode.
To achieve the above object, a portable information terminal according to the present invention has a detector for detecting a radio wave sent from a mobile telephone set and generating a power supply voltage from electric energy extracted from the radio wave.
If there is no process to be carried out by the portable information terminal, then the portable information terminal is brought into a standby mode, and the supply of a main power supply voltage from a main power supply to various parts of the portable information terminal is stopped. A connector operates under the power supply voltage generated by the detector, and instructs the main power supply to supply the main power supply voltage to the various parts of the portable information terminal when it receives an indication to start data communications from the mobile telephone set.
In the standby mode, the portable information terminal operates under only the power supply voltage generated from the electric energy that is extracted from the radio wave sent from the mobile telephone set. Therefore, the portable information terminal does not consume the electric energy of the main power supply, which typically comprises a battery.
The portable information terminal may be placed into the standby mode upon detection of the elapse of a preset period of time in which no process has been performed by portable information terminal.
After the portable information terminal is brought from the standby mode into the normal mode to start the data communications, the portable information terminal may be immediately brought back into the standby mode in response to completion of the data communications.